1. Field of the Invention
The present invention concerns a method of manufacturing a semiconductor device having a field effect transistor, and the semiconductor device.
2. Description of Related Art
In metal-oxide-semiconductor field effect transistors (MOSFETs), there is a technique of using an insulation layer having a higher dielectric constant (High-k material) than SiO2 or SiON as a gate insulation film and using a metal or a metal nitride as a gate electrode. This technique can improve the current driving performance.
IEEE Electron Device Letters, vol. 25, No. 5, 2004, pp 337 to 339, written by H. Y. Yu (Non-patent document 1) describes use of an Si/metal nitride film where Si is stacked on a metal nitride film as a gate electrode.
2008 Symposium on VLST Technology Digest of Technical Papers, pp 48 to 49, written by M. Kadoshima, et al. (Non-document 2) describes that an apparent work function of a gate electrode can be controlled by adjusting the thickness of a metal nitride film used for a gate electrode. Specifically, the non-patent document 2 describes that an apparent work function of the gate electrode increases as the thickness of a metal nitride film used for the gate electrode increases more. When the apparent work function of the gate electrode increases, a threshold voltage Vt of pMOSFET is lowered (absolute value for negative Vt value is decreased) as the apparent work function of the gate electrode increases and the threshold voltage Vt of nMOSFET increases (absolute value for positive Vt value is further increased). The non-patent document 2 describes that a CMOSFET in which both of a pMOSFET and an nMOSFET have lower threshold value voltages (small absolute value for Vt value) by controlling the threshold voltage Vt depending on the thickness of the metal nitride film.